Ecological Restoration Programs Research Articles

Untangling the effects of management measures, climate and land use cover change on grassland dynamics in the Qinghai–Tibet Plateau, China

AbstractMultiple large‐scale ecological conservation programmes have been launched by the Chinese Government to combat grassland degradation across the Qinghai–Tibet Plateau (QTP) since 1999. However, the mechanisms by which these ecological initiatives might affect grassland changes remains unknown. Here, we examined the land use cover change (LUCC) and net primary productivity (NPP) of the grassland in the QTP in 2001–2016. The effects of LUCC, management measures, and climate variation on grassland NPP were quantitatively evaluated. The grassland area had a net increase of 96,397 km2, which could be attributed to the conversion of desert and forests. The total NPP of grassland increased by 154,073.7 GgC·yr−1 in 2001–2016, of which the contribution of climate and human factors occupied 35.58% and 64.42%, respectively. Specifically, climate variation caused an overall increase of 54,823.24 GgC·yr−1in grassland total NPP. The climate‐dominated NPP decrease was widely found in the eastern and southern QTP. The contribution of LUCC and management measures to the increase of grassland NPP was 62.78% and 37.22%, respectively. This increase was mostly found in the mid‐east region of the QTP, which could sufficiently counteract the negative effect of climate variation on NPP. Overall, these findings seem to demonstrate that these ecological restoration programs have substantially promote the increase of grassland NPP and contribute to understanding the degree to which the grassland ecosystem may respond to the LUCC and management measures under the ecological restoration projects, which are essential to developing more effective ecological measures for future grassland restoration in the QTP.

The use of state‐and‐transition models in assessing management success

AbstractState‐and‐transition models (STM) are valuable tools that aid understanding and management of ecosystems. There also is potential for STMs to be used as a framework to assess whether management actions are achieving desired conservation objectives. However, few published examples exist where STMs have been used in this way. Using high‐quality empirical field data collected in endangered temperate woodlands across a 6‐year period, we explore whether a Box Gum Grassy Woodland STM employed in an Australian agri‐environment scheme can be used to assess whether management interventions are achieving an improvement in woodland Condition State. We found there was insufficient contextual information in the STM to facilitate its robust use as a framework for assessing whether management interventions were achieving conservation outcomes in Box Gum Grassy Woodlands. Weather was a key driver influencing management effectiveness, but its effects were absent from the STM, as were probabilities and time frames for transitions between Condition States. The deficiencies in the STM may preclude accurate conclusions about the effectiveness of the program. Given the influence of weather on the system, longer time frames are required to adequately assess the influence of management on key variables (e.g., native plant richness, native ground cover) underpinning the STM. This case study provides opportunities to understand the potential implications of using insufficiently contextualized STMs as frameworks for assessing whether management actions are achieving desired conservation objectives. It also provides opportunities to learn from what went wrong. To this end, based on our findings, we provide practical recommendations (applicable beyond our case study system) for improving the construction and implementation of STMs for the purposes of evaluating the success of management interventions in ecological restoration and conservation programs.

Do ecological restoration programs reduce forest fragmentation? Case study of the Three Gorges Reservoir Area, China

Ecological restoration programs (ERPs) have greatly expanded forested areas in China to mitigate environmental problems. Unfortunately, this general increase in forest cover has not revealed clear changes in the states of fragmentation and loss of connectivity of forested habitats, and few studies have investigated the effects of ERPs on the spatial patterns of forests. Taking the Three Gorges Reservoir Area as a case study, we assess and quantify how the dynamics of the spatial patterns of forest following massive ERPs from 1990 through 2015 by morphological spatial pattern analysis (MSPA). We examine possible landscape structure thresholds in the forest restoration gradient. The results indicate that dramatic decreases in forest fragmentation and patchiness have occurred since ERP implementation. Among the seven MSPA forest types, core forests show the highest increase of 513.91 km2·yr−1. ERPs promote the defragmentation of forests via two pathways: (1) Old forests are preserved and expanded by building new forests around existing patches and closing perforations within forests; and (2) new core forests are gradually created in areas far from older forests. However, isolated forest patches surrounded by cropland production areas formed after the conversion of croplands into forests have appeared across the study area. Furthermore, at least two points of nonlinear changes in the landscape structure with increasing forest cover are identified. These nonlinear trajectories can be used as indicators of critical shifts in ecosystem states, and relevant thresholds support the identification of specific conservation actions. Our findings demonstrate the importance of ERPs for the defragmentation of forest patches and provide a basis to establish a more effective arrangement of patches necessary to mitigate fragmentation effects. Given that landscape structural changes are not expected in ERP design, future ERPs should focus on remaining isolated forest patches and on maintaining the health and sustainability of landscapes.

Potential risk to water resources under eco-restoration policy and global change in the Tibetan Plateau

Water shortage is a core problem that has hindered sustainable development worldwide. The Tibetan Plateau feeds ten main rivers on which almost 20% of the world’s population depends. However, the plateau has suffered serious environmental deterioration from global warming. Since the 1980s, the Chinese government has supported ecological restoration in the Tibetan Plateau, mainly by promoting large-scale afforestation and grassland conservation. To identify the impact of global change and ecological restoration policy on the plateau, we used geographic information system (GIS) methodologies to study changes to the water supplies in the region as a result of implemented restoration programs. Moreover, we also used GIS to assess the potential risks of these changes for the long-term sustainability of water supplies. Our findings show that the quantity of water supplies in the Tibetan Plateau has increased over the last 36 years; this was attributed to an increase in precipitation as well as increasing glacial meltwater due to global warming. We also found that the water consumption associated with afforestation projects reduced the water yield, in that it was altered by the artificial establishment of plant communities, with different afforestation projects variously impacting water consumption. The potential risk areas in the plateau were mainly distributed in areas with dense human populations and villages, and intensive human activities around forest shrubs where ecological restoration programs had been largely implemented. We highlight the need for ecosystem management and monitoring within larger afforestation programs, which should include the planting of vegetation with low rates of water consumption.

Landscape configuration mediates hydrology and nonpoint source pollution under climate change and agricultural expansion

Climate variability and landscape modifications directly influence watershed hydrology and processes of nonpoint source pollution, while remedial action requires distinguishing their effects. However, nonlinearity and multiple causality limit our ability to diagnose causes. Therefore, this study developed an approach that integrates hydrological modeling, random forests, regression trees, and variation partitioning analysis, to identify the effects of climate and landscape pattern changes upon runoff and nitrate loading in two typical watersheds in the Three Gorges Reservoir area of China. The Soil and Water Assessment Tool (SWAT) was used to track the spatiotemporal dynamics of runoff and nitrate loading (2000–2015). The findings showed that drylands and orchards were the dominant sources of nitrate and baseflow was the key mode of nitrate transport. Water yield and baseflow were mainly influenced by precipitation change, while the surface runoff and nitrate load were affected primarily by landscape pattern changes, especially in the wet season. Although ecological restoration programs have improved forest cover and forest fragmentation, the effects of forest restoration on the reduction of surface runoff and nitrate at the watershed scale have been offset by increased precipitation and agricultural expansion. Nevertheless, the role of landscape configuration is so dramatic that it can override variation in nitrate losses driven by changes in land cover and precipitation. Effective control of nitrate loss under intensive ecological restoration can be achieved by using a mosaic of “sink” patches to divide larger areas of cropland into smaller patches, maintaining cropland fragmentation, and limiting the increase in edge density of cropland. This paper’s proposed and implemented approach provides a new understanding of the interactions and nonlinear relationship between hydrological processes and environmental change, providing explicit ideas and useful insights for landscape planners and managers for improving eco-hydrological functions of watershed at the practical level. We emphasize that the impact of land use change cannot be assumed to be linear in restoration strategies, instead nonlinear impacts, clear details of landscape configuration, and seasonal climatic characteristics should be explicitly considered.

Ecological restoration policy should pay more attention to the high productivity grasslands

To address severe grassland degradation problems, China has been implementing several national restoration programs, which have been reported to mitigate the deterioration of grassland ecosystem function. However, the regional differences in the effectiveness of the programs are not yet known. In this study, gross primary productivity (GPP) was selected as an indicator to analyze grassland degradation dynamics, and the residual trend method was used to assess the driving force of grassland degradation based on GPP. The results showed the GPP of Inner Mongolia grassland significantly increased by 3.94 g C m−2 yr−1 during 2000–2015, climate change was the dominant driving factors, while human activities slightly reduced grassland productivity (−0.17 g C m−2 yr−1). But there are obviously spatial heterogeneous on the impact of human activities. Specifically, grassland management significantly promoted the GPP increase in semidesert steppe, while grazing activity decreased the GPP in meadow and typical steppes. These findings suggest that ecological restoration programs could obviously improve vegetation functioning in ecologically fragile grassland which has relatively very low productivity. However, the grasslands with relative higher productivity or initially non-degraded are still facing with great degradation risk due to the continuous growing livestock scale. Therefore, policy-makers should pay more attention to the originally non-degraded or high productivity grasslands, especially at those years the negative impacts of intensive grazing could be concealed by the well-growth grass under abundant precipitation.

A framework for calculating the net benefits of ecological restoration programs in China

Information about the costs and benefits of the land use changes that occur during the implementation of ecological conservation programs is still scarce. To obtain more information on these consequences, it’s necessary to compare the costs and benefits before and after project implementation. We have proposed a modification of the framework for calculating this change in the net benefits of ecological engineering, using implementation of China’s primary conservation programs to demonstrate the framework. We found that the annual net benefits created by the Three North Shelter Forest System Project, Natural Forest Conservation Program, and Grain for Green Program in 2017 were 461.7 × 109, 2930.5 × 109, and 530.1 × 109 RMB, respectively; these are equivalent to net benefits per unit area of 6.5 × 103, 17.6 × 103, and 18.2 × 103 RMB·ha−1·yr−1. These values represent rates of return equal to 29.3, 328.9, and 77.0%, respectively, compared with the costs of these investments. Due to the large differences in socioeconomic conditions and resource endowments among China’s diverse regions, it is necessary to account for these regional differences in the design of ecological restoration strategies to ensure that the programs are tailored to local conditions and produce the maximum net benefit. This approach can help governments find an optimal combination of land use and ecological conservation to improve the economic impacts of their restoration programs.

Spatiotemporal Pattern of Pine Wilt Disease in the Yangtze River Basin

The Yangtze River Basin is among the river basins with the strongest strategic support and developmental power in China. As an invasive species, the pinewood nematode (PWN) Bursaphelenchus xylophilus has introduced a serious obstacle to the high-quality development of the economic and ecological synchronization of the Yangtze River Basin. This study analyses the occurrence and spread of pine wilt disease (PWD) with the aim of effectively managing and controlling the spread of PWD in the Yangtze River Basin. In this study, statistical data of PWD-affected areas in the Yangtze River Basin are used to analyse the occurrence and spread of PWD in the study area using spatiotemporal visualization analysis and spatiotemporal scanning statistics technology. From 2000 to 2018, PWD in the study area showed an “increasing-decreasing-increasing” trend, and PWD increased explosively in 2018. The spatial spread of PWD showed a “jumping propagation-multi-point outbreak-point to surface spread” pattern, moving west along the river. Important clusters were concentrated in the Jiangsu-Zhejiang area from 2000 to 2015, forming a cluster including Jiangsu and Zhejiang. Then, from 2015–2018, important clusters were concentrated in Chongqing. According to the spatiotemporal scanning results, PWD showed high aggregation in the four regions of Zhejiang, Chongqing, Hubei, and Jiangxi from 2000 to 2018. In the future, management systems for the prevention and treatment of PWD, including ecological restoration programs, will require more attention.

Conservation of the Tropical Rainforest in the Usumacinta Canyon Flora and Fauna Protection Area in Mexico

Objective: To study the conservation status of the tropical rainforest in the “Cañón del Usumacinta” Flora and Fauna Protection Area in Mexico, through an analysis of the change in land use and vegetation (1997, 2009 and 2016). Design/Methodology/Approach: Vegetation and land use shapefiles at 1:250,000 scale (national continuum) corresponding to 1997 (series I), 2009 (series IV), and 2016 (series VI) were downloaded. Finally, a spatial analysis was generated with calculation of exchange rates, using the Land Change Modeler between 1997-2009 and 2009-2016. Results: During 1997-2009, the tropical rainforest occupied 31.2% and the greatest impact of the period seen was a change rate of 7.4%. Subsequently, between 2009 and 2016 there was a great decrease in the land use change rate in the forest (0.8%), due to its decree as a federal Protected Area in 2008, as well as natural regeneration and the promotion of ecological restoration programs. Study Limitations/Implications: Absence of geographic variables to analyze factors driving change in land use. Conclusions: It is essential to promote the sustainable management of the Usumacinta Canyon based on what is established in the land use planning program and the management plan, and to redouble efforts to implement actions for restoring ecosystem services and the continuous monitoring of change in land use.

Vegetation restoration projects intensify intraregional water recycling processes in the agro-pastoral ecotone of Northern China

AbstractFrom 1998 to the present, the Chinese government has implemented numerous large-scale ecological programs to restore ecosystems and improve environmental protection in the agro-pastoral ecotone of Northern China (APENC). However, it remains unclear how vegetation restoration modulates intraregional moisture cycles and changes regional water balance. To fill this gap, we first investigated the variation in precipitation (P) from the China Meteorological Forcing Dataset and evapotranspiration (ET) estimated using the Priestly-Taylor Jet Propulsion Laboratory model under two scenarios: dynamic vegetation (DV) and no dynamic vegetation (no-DV). We then used the dynamic recycling model to analyze the changes in precipitation recycling ratio (PRR). Finally, we examined how vegetation restoration modulates intraregional moisture recycling to change the regional water cycle in APENC. Results indicate P increased at an average rate of 4.42 mm yr-2 from 1995 to 2015. ET with DV exhibited a significant increase at a rate of 1.57, 3.58, 1.53, and 1.84 mm yr-2 in the four subregions, respectively, compared with no-DV, and the annual mean PRR values were 10.15%, 9.30%, 11.01%, and 12.76% in the four subregions, and significant increasing trends were found in the APENC during 1995-2015. Further analysis of regional moisture recycling shows that vegetation restoration does not increase local P directly, but has an indirect effect by enhancing moisture recycling process to produce more P by increasing PRR. Our findings show that large-scale ecological restoration programs have a positive effect on local moisture cycle and precipitation.

3D-CNN based UAV hyperspectral imagery for grassland degradation indicator ground object classification research

The identification and counting of grassland degradation indicator ground objects is an important component of grassland ecological monitoring. These steps are also an important basis for developing ecological restoration and management programs for degraded grasslands. Compared with a traditional human survey, the use of remote sensing images can not only achieve dynamic monitoring of a large area, but also improve the efficiency. Recently, most studies regarding ground object classification based on remote sensing images address the development and optimization of classification models for features in several widely used datasets. For the remote sensing of desertified grasslands, remote sensing images with high spatial resolutions are used for studies on small and sparse features in degraded grasslands. The spatial resolution of the above mentioned datasets yields difficulties when attempting to classify small and sparse indicator features for desertified grasslands because generalization becomes limited. Therefore, establishing a lightweight classification model suitable for degraded grassland features with high spatial resolution is important. In this study, a low altitude unmanned aerial vehicle (UAV) hyperspectral remote sensing platform was constructed to collect high spatial resolution remote sensing images of degraded grasslands. The GDIF-3D-CNN classification model was used to classify the pure pixels and all pixels datasets, whose accuracy and efficiency were further improved by optimizing the eight parameters of the model. This study explores the remote sensing ground object classification of thin small plants and a large number of mixed pixels, realizing high precision classification among desertification degradation indicating plant populations of a species, and provides key quantitative data for grassland degradation research.

How Environmental Awareness and Knowledge Affect Urban Residents’ Willingness to Participate in Rubber Plantation Ecological Restoration Programs: Evidence from Hainan, China

The rapid expansion of rubber plantations in Asian countries has led to various environmental problems. Therefore, local governments are implementing rubber plantation ecological restoration (RPER) programs as an essential solution. However, such programs can be implemented only if residents are intensely involved. Based on a survey of 521 urban households in Hainan Province, China, this study investigates the effect of environmental awareness and knowledge on residents’ willingness to participate in RPER programs. We employ a double-hurdle (DH) model to estimate residents’ participation in two stages. First, we determine whether residents wish to participate or not (PN). Then, we measure residents’ degree of willingness to participate (DWP). The results show that residents’ environmental awareness has a significant positive effect on whether they wish to PN but has no impact on their DWP. By contrast, residents’ environmental knowledge has a significant positive effect on whether they wish to PN and their DWP. The moderating effect shows that residents’ environmental knowledge significantly weakens the positive effects of their environmental awareness on whether they wish to PN. Moreover, residents’ age, educational level, employment, and place of residence substantially influence their DWP. The findings in this study can provide useful insights for policymaking on improving rubber plantation ecosystems.

Effects of anthropogenic revegetation on the water and carbon cycles of a desert steppe ecosystem

The anthropogenic revegetation for combating desertification in China has been a long-term strategy that has induced shrub encroachment in desert steppe and regionally notable greening. Although the benefits of reversing desertification, preventing erosion, and providing biomass have been recognized, the effects of anthropogenic revegetation on water and carbon cycles, the critical process of terrestrial ecosystem, are still poorly understood. This study evaluates the effects of anthropogenic revegetation on water and carbon cycles in a typical desert steppe located in Yanchi County, Ningxia Province, Northwest China, by simulating two scenarios of grassland and shrub with the Biome-BGC model. Continuous CO2 and H2O flux measurements from 2016 to 2019 were used to validate the performance of Biome-BGC. Results showed that the anthropogenic revegetation significantly intensified the carbon cycle and increased carbon storages in the ecosystem and transformed the desert steppe ecosystem from a weak carbon source into a strong carbon sink. At the same time, the anthropogenic revegetation critically increased the water consumption of the ecosystem and decreased the soil water storage. The extreme consequence would be that the water resource will exceed the sustainable limit of ecosystems in the context of precipitation as the only water supply. Such undesired outcomes should be given more attention in state and local ecological restoration programs.

Mapping mangrove forests in the Red River Delta, Vietnam

Mangrove forests (MFs), which occur along tropical and subtropical coastal zone, are among the most productive and richest carbon-rich ecosystems in the world. However, MFs have experienced great losses worldwide due to the impacts of intensive human activities and relative sea level rise. Here, the recent dynamic changes in the MFs of the Red River Delta (RRD), the second largest delta in Vietnam, were quantified using the random forest algorithm based on 328 remote images obtained by Landsat TM/ETM+/OLI during 1986–2019. The results show obvious increasing trends in the MF area with a change rate of 39 ha/y from 1,655 ha in 1986 to 2,944 ha in 2019. The change rates in the northern RRD (NP) and southern RRD (SP) were 8.44 ha/y and 30.62 ha/y, respectively, even though MFs in the tropics worldwide encountered significant losses. Further, approximately 1,091 ha of MF was converted into aquaculture ponds during 2000–2006 in the interior of the RRD, while the shoreline of MFs in the NP and SP continually expanded seaward to the northeast and southwest at average rates of 38.9 m/y and 17.9 m/y, respectively. Moreover, although the fluvial sediment supply declined dramatically from 199.57 to 16.41 mt/y during 1986–2017, the sediment supply was not responsible for the present seaward expansion of MFs. Wave action drove sediments to overwash barriers, and tidal dynamics carried this sediment into tidal channels, depositing sediments behind the barriers and on both sides of tidal channels with continuing MF growth. In addition, the conversion of MFs into aquaculture ponds by human activities was responsible for the massive losses of MFs in 2000–2006, but these impacts were alleviated as conservation policies were implemented by local governments in subsequent years. This study indicates that the growth, loss and recovery of MFs are affected by various factors, and it is vital to map the variations in MFs to better implement regional ecological restoration programs for coastal MFs.

Population increase and changes in behavior and morphology in the Critically Endangered Redonda ground lizard (Pholidoscelis atratus) following the successful removal of alien rats and goats.

Redonda is a small volcanic Caribbean island that is home to at least 4 endemic lizard species, including the Critically Endangered ground lizard (Pholidoscelis atratus). Black rats (Rattus rattus) and domestic goats (Capra hircus) were introduced to the island at some time after its discovery by Europeans in the late 1500s. They had a devastating effect on the island, resulting in the loss of nearly all trees and most of the ground vegetation. Point count surveys of P. atratus in 2012 indicated low densities, and the invasive rats were observed hunting and preying on the lizards. Both populations of rats and goats were successfully removed in 2017 as part of an ecological restoration program, and native vegetation and invertebrate populations have increased rapidly since. Population surveys in 2017, 2018, and 2019 show the lizard population has increased by more than sixfold. In 2017, as rats and goats were being removed, we evaluated the morphology and escape behavior of this species and repeated these measurements 1 year later. We observed that P. atratus had become bolder, with a reduced flight distance. We also detected changes in limb morphology related to locomotion and suggest possible explanations that will need to be further investigated in the future. These results show how the removal of invasive species can rapidly affect lizard population recovery and behavior, potentially restoring island ecosystems to their pre‐human interference dynamics.

Seed germination of six Iberian endemic species – a contribution to enhance plant conservation

Biodiversity has been degraded all around the world due to anthropogenic factors. To counteract this worldwide tendency, ecological restoration programs are expanding. In these programs, the use of native herbaceous species, particularly those endemic or threatened, can be promoted by seeding them but germination requirements for most of these species are unknown. Our research meant to fill this gap of information for six Iberian endemic species suitable to use in restoration actions - Digitalis thapsi, Ferula communis subsp. catalaunica, Linaria amethystea subsp. amethystea, Pterocephalidium diandrum, Sanguisorba hybrida, and Silene scabriflora subsp. scabriflora. Their seed germination behaviour was analysed to establish germination protocols for conservation actions. Three germination conditions were used to simulate different sown seasons. Seeds of all species were tested without pre-treatment and subjected to a cold stratification. Seeds of S. hybrida and P. diandrum were additionally tested with a scarification treatment. All species reached their better germination performance under autumn conditions (15/10 °C; 8/16 hours). In conclusion, for all the six Iberian endemic species tested, germination speed and percentage were suitable for their use in native plants reinforcement.

Carbon sequestration benefits of the grain for Green Program in the hilly red soil region of southern China

Soil erosion disturbs not only the global carbon cycle, but it is a complex environmental problem. Revegetation could reduce carbon emission by controlling soil erosion and increase carbon sequestration and accumulation by fixing carbon in vegetation and soil. The Grain for Green Program (GFGP) of China is the largest ecological restoration program in the world closely related to land-use/land-cover change (LUCC). Systematically assessing the carbon sequestration benefit of GFGP is crucial for a better understanding of the effects of implementing GFGP and providing reasonable vegetation management. Therefore, we selected the hilly red soil region (HRSR) of southern China as a study area, which is one of the main ecologically vulnerable areas in China. We assessed the carbon sequestration in the GFGP area of the HRSR using the InVEST (Integrated Valuation of Environmental Services and Tradeoffs) model based on land-use/land-cover datasets during 2000–2015. Our results show that implementing GFGP is conducive to the enhancement of carbon sequestration services. Total carbon sequestration showed an increasing trend at a rate of 15.43% from 2000 to 2015. The most significant change mainly happened in Hunan Province with the shortest implementation time. The carbon sequestration of each carbon pool (namely aboveground biomass, belowground biomass, soil, and dead organic matter) also increased slightly. Additionally, for carbon sequestration, unused land converted to forest land is the most effective LUCC. This study can provide scientific support for the management and implementation of GFGP in the HRSR of China.

Impacts of land-use conversions on the water cycle in a typical watershed in the southern Chinese Loess Plateau

Land use change is one of the dominant driving factors of hydrological change at the watershed scale. Thus, understanding the hydrological responses to land use changes can facilitate development of sustainable water resource management. The land use of the Wei River (the largest tributary of the Yellow River) Basin (WRB) has changed greatly due to the large-scale ecological restoration program in the Chinese Loess Plateau (e.g., grain-for-green program), causing dramatic impacts on the water cycle. This study was to simulate the impacts of land use and land cover change (LUCC) on the key hydrological components, using the Soil and Water Assessment Tool (SWAT). We investigated the spatiotemporal changes of LUCC from 1980 to 2010 in terms of four sub-regions (i.e., three subbasins and one mid-downstream area) and three landforms (i.e., mountain, hill, and plain), respectively. Then, we quantified the spatial heterogeneity of hydrological responses to land use change scenarios. Our LUCC analysis showed that cropland declined by about 0.8%, from 58,776 km2 in 1980 to 57,519 km2 in 2010, whereas the forest and grassland areas correspondingly increased 552 km2 and 16 km2, respectively. The urban area changed more dramatically in the middle and lower reaches of the Wei River owing to the faster socioeconomic development in this region than the rest areas. In mountain area, the main types of land use were forest and grassland, and the main transformation was from cropland to forest land and grassland. The area of cropland in plain could be over 50%, and it was mainly converted to urban land. The hydrological simulation indicated that LUCC from 1980 to 2010 caused 5.3% of decrease in the water yield and 6.2% increase in soil water content, but there was nearly no change in evapotranspiration (ET). Scenarios about slopping land use conversion (SLC) program showed that the conversion of cropland to grassland or forest (i.e., grain-for-green) resulted in negative effects on soil water content and water yield, with a greater effect by the reforestation. In addition, we found that the change of ET was clear in areas where cropland with slope > 15° was converted to grassland or forest, suggesting slope is also an important factor for hydrological responses to LUCC. This study can provide valuable decision support for land use planning and water resources protection in the WRB.

The relative contribution of vegetation greening to the hydrological cycle in the Three-North region of China: A modelling analysis

China has implemented a few large-scale afforestation programs in the arid and semi-arid areas, including the north-eastern, northern, and north-western regions, collectively referred to as the Three-North region (TNR), to combat desertification and control dust storms. Although these programs have alleviated environmental problems in the region to a certain extent, the effects of increasing vegetation greenness on the hydrological cycle remain controversial. In this study, the relative effects of afforestation programs on the hydrologic processes in the TNR were identified based on large-scale hydrological modeling and satellite remote sensing data. The model forcing was featured with long-term vegetation dynamics. The study period ranged from 2000 to 2015, during which the greening of vegetation in the TNR was increased after multiple afforestation programs were carried out around 2000. The results indicated that, despite the spatial heterogeneity, the vegetation leaf area index (LAI) exhibited a significant increase across the TNR. Evapotranspiration (ET) increased over the entire region at the rate of 2.9 mm/year from 2000 to 2015, and its spatial pattern was consistent with changes in the LAI and precipitation. However, this does not imply equal contribution by vegetation growth and precipitation change. The results from the simulation scenarios indicated that precipitation change had a more significant influence on the ET, soil moisture and runoff than vegetation growth at the regional scale. Vegetation greening and precipitation increase in the Loess Plateau indicated their approximately equal impacts on ET and soil moisture. Consequently, the hydrological cycle was sensitive to afforestation practices at small-catchment or sub-regional scales where the magnitude of vegetation greening is relatively high. Therefore, the hydrological effect of vegetation greening at large scale may be overestimated by previous studies. To ensure sustainable water resource management at the TNR scale, special attention should be paid to climate change rather than afforestation efforts under the current level of ecological restoration programs.

Positive effects of ecological restoration policies on the vegetation dynamics in a typical ecologically vulnerable area of China

Ecological restoration programmes have been initiated worldwide because of serious environmental degradation. However, the effectiveness of ecological restoration remains contentious because vegetation restoration is impacted by both climate change and human activities. Climate change is an important factor for vegetation restoration, especially in ecologically vulnerable areas. The Zhangjiakou region of northern China is located in a semiarid and subhumid climate region with apparent ecosystem vulnerability. Since the late 1970s, a series of ecological restoration programmes have been carried out in this area to recover the vegetation and ecosystems. Based on remote sensing images and ground-based meteorological data, two vegetation indexes (NDVI and EVI2) and aridity index were calculated to analyse (i) the vegetation dynamics and climate aridity trends in the Zhangjiakou region and (ii) the response of the vegetation dynamics to ecological restoration programmes and climate change between 1987 and 2017. The results indicated that vegetation cover increased with twice abrupt changes in 2002 and 2009, respectively, which simultaneously underwent an increase in aridity. Vegetation cover has increased rapidly since 2003 because of ecological recovery projects and policies. The contributions of climate change and human activities to vegetation cover were12%~ 5.2% and 88% ~ 94.8% during the period 2003–2009, respectively. The contributions of climate change and human activities to vegetation cover were2.1% ~ 2.4% and 97.9% ~ 97.6% during the period 2010–2017, respectively. The ecological restoration projects and policies effectively promoted vegetation cover in the study area.